Where to add the Licence Key

Hello,

I got premium and well received the Licence Key in the invoice by email.
My (stupid) question is where to add this licence key ?
I guess it’s in the settings ? But ALL categories of settings (premium, other’s, permalinks etc) are BLANK.

I have try with Chrome (to change from Safari), it’s the same.
I have uninstall the plug-in and re-install from a zip downloaded. Still the same.

Thanks for your help.

Best Regards to all

Arnaud